1. Field of the Invention
The present invention relates in general to gas turbines. In particular, it relates to- a platform cooling system having a guide-blade platform which is subjected to a hot-gas stream and is separated by a gap from a combustion-chamber segment arranged upstream.
2. Discussion of Background
In order to achieve a maximum turbine output, it is advantageous to work at the highest possible gas temperatures. In modern gas turbines, the temperatures are so high that many components have to be cooled, since otherwise the temperature of the components which is permissible for maximum durability would be exceeded. A suitable design and/or cooling of critical components is therefore of crucial importance in modern gas turbines. The cooling problem of platforms occurs to an increased extent in annular combustion chambers, since the latter produce a very uniform radial temperature profile at the entry to the turbine.
On account of the radially more uniform temperature profile at the turbine inlet, the thermal loading of the turbine components attached there, such as, for instance, the platforms and shroud bands, increases. In particular the platforms of the inlet guide blades directly at the turbine inlet are subjected to an extremely high thermal stress. From the combustion chamber, hot gas penetrates into the intermediate spaces between the last combustion-chamber segments and the platforms of the inlet guide blades and loads the components there to a considerable extent. Whereas the blades and the surfaces directly subjected to the hot-gas stream are adequately cooled as a rule and are made of temperature-resistant materials, this often does not apply to the inner surfaces of the gap. This leads to a reduced service life, and often also to damage to the components adjoining the gap. On the other hand, if the operating temperature of the hot gas is reduced, this results in reduced efficiency of the turbine.